(a) Technical Field
The present invention relates to a device and a method for monitoring dryness of a fuel cell stack, more particularly, to the device and the method for monitoring dryness, which make it possible to accurately determine whether the fuel cell stack is dry or not.
(b) Description of the Related Art
A fuel cell, which is a type of power generation device for generating electricity that is the energy source of fuel cell vehicles, has a structure in which an anode to which hydrogen is supplied and a cathode to which air is supplied are stacked with an electrolyte assembly therebetween, and generates electricity using a chemical reaction between the oxygen in the air and the hydrogen supplied from the outside.
A fuel cell is manufactured in a fuel cell stack with tens to hundreds of unit cells stacked, and the configuration of one unit cell is described hereafter with reference to FIG. 5 (RELATED ART).
First, a membrane-electrode assembly (MEA) is disposed at the innermost part of the fuel cell stack, and is composed of a polymer electrolyte membrane 10 allowing hydrogen protons to move and catalytic layers applied to both sides of the electrolyte membrane to allow a reaction of hydrogen and oxygen, that is, a cathode 12 and an anode 14.
Further, gas diffusion layers (GDLs) 16 are disposed at the outer part of the fuel cell stack where the cathode 12 and the anode 14 are positioned, separators 20 having a flow field to supply fuel and discharge water produced by a reaction are disposed outside the GDLs 16, with gaskets 18 therebetween, and end plates 30 for supporting and fixing these components are disposed at the outermost sides.
Accordingly, an oxidation reaction of hydrogen occurs and thereby protons and electrons are produced at the anode 14 of the fuel cell stack, the protons and electrons move to the cathode 12 through the electrolyte membrane 10 and the separator 20, respectively, and at the cathode 12, water is produced by an electrochemical reaction of the protons and electrons which have moved from the anode 14 and the oxygen in the air and simultaneously electric energy is generated by flow of the electrons.
The fuel cell stack needs to be as humid as possible, because the protons can move well to the cathode from the anode through the electrolyte membrane when the fuel cell stack is in a humid state.
When the fuel cell stack is dry, the electrolyte membrane is dry and protons cannot move well accordingly, so problems such as generally decreasing the performance of the fuel cell including drop in voltage generated by the stack and the like.
When the electrolyte membrane is repeatedly dried and humidified, durability of the electrolyte membrane decreases.
In the meantime, the amount of air to the amount of water produced in the stack in the operation of the fuel cell stack is basically large, because the end cells of a plurality of cells in the stack or a common distributor connected to the end cells cause flooding that is a phenomenon in which the cells are filled with the produced water if an amount of air is small.
Accordingly, when current load is generated under the condition of a flooding phenomenon, it negatively influences the durability of the cells, so in order to prevent this influence, a larger amount of air than the produced water is supplied into the stack to keep a larger amount of air than the produced water in the stack.
As a larger amount of air than the produced water resulting from a reaction in the stack is supplied, the entire stack is necessarily kept dry, and as described above, when the stack is dry, protons cannot move well, so that performance of the stack is deteriorated and the durability of the electrolyte membrane decreases.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.